How to copy pose onto different legs of spider?
In Pose mode select all the bones of the leg you've already animated. In the Dope Sheet enable the Only Show Selected option and copy the keyframes. Select all the bones of another leg, create one keyframe (I don't know why it's necessary though) and in the Dope Sheet paste the keyframes previously copied. As the 000 location of a bone depends on its location set in Edit mode and not on its location in the global space, the second bone won't jump to the first bone location, it will just copy the animation but stays at its current location.